Method of preserving and fireproofing a structural member and resultant article



Aug- 27, 1957 R. M. HOOKS 2,804,398

METHOD OF' FRESERVING AND FIREPROOEING A STRUCTURAL MEMBER AND RESULTANT ARTICLE Filed Nov 22, 1954 llllllllllll FIELE.

United States Patent Otice 2,804,398 Patented Aug. 2'77, 1957 Robert M. Hooks, Fort Worth, Tex., assigner to Sonth- Western Petroleum Co., Inc., Fort Worth, Tex., a corporation of Texas Application November 22, 1954, Serial No. 470,525

4 Claims. (Cl. 117-72) This invention relates to the proofing of structures against the hazard of tire. It has particular reference to the proofing of timbers and similar structural units of wood which have been treated with preservative. This is a continuation-in-part of my application Serial No. 320,618, tiled November 14, 1952, now abandoned.

Wood structural units such as ties, piles, rails, planks, etc., used widely by railroads are customarily treated with some sort of preservative composition. One satisfactory preservative comprises la coal tar creosote-petroleum oil mixture which is impregnated into the wood under pressure to the quantum extent of about eight pounds of the preservative oil to one cubic foot of wood. Frequently the wood is subjected to the preservative treatment within a relatively short time before use must be made of it, thus preventing complete absorption into the pores of the wood and causing a residue of the preservative iiuid to remain more closely adjacent the surface of the wood than is desirable.

The fire hazard to wooden structures along railroad rights of way are well known and varied. Grass tires and the like are by no means unusual `and it is impossible to maintain constant watch over the long stretches which are subject to such hazard.

In the past it has been customary to use a coating of some bituminous substance, usually formulated with an asphaltum base, for coating purposes to guard against the hazard of fire. Various modifications of these asphaltum base coatings have been developed to make them more resistant to heat and prevent flow of the coating material under the iniiuence of heat to thereby expose the wood. Such procedures have proved successful under ordinary circumstances.

But where the wood is impregnated under pressure with a large volume `of coal tar creosote-petroleum oil mixture, a serious problem arises. Such a mixture is composed of approximately 50% creosote and 50% petroleum oil, or in some cases 70% petroleum oil and 30% creosote. 4 Where such a preservative in such a large quantity is impregnated in the wood, ithas been found that no known type of asphaltum base coating is completely insoluble when contacted by the preservative oils, especially on exposure to heat. The preservative oils have a ash point of approximately 235 F. and a lire point of approximately 255 F. The oils are extremely volatile and iniiammable when exposed to heat and these properties enable them to remove nearly any bituminous coating from the surface of wood. The effectiveness of an ordinary `bituminous base coating is eliminated as the coating material dissolves and is forced from the surface of the wood by evolution of gas. j

An object of this invention is to eliminate not only the tire hazard provided by the use of wood, but the extra re hazard created by pressure impregnation in large quantums with preservative compositions having relatively low flash and fire points. t

A further and more specific object resides inl providing a coating for wood 'impregnated as heretofore described which, when subjected to pressure of gas evolution from within, will yield without rupture and separate from the wood surface, thereby reducing the temperature at the surface of the wood and preventing destructive distillation and charring of the wood.

A solution of the problem, such as that described above, has many benefits and is far superior tovarious other procedures which have been used in seeking to overcome the difficulty. Some success has been obtained by completely covering a wooden structure with a glass fabric or mat to support coatings of either a bituminous or an inorganic cement type. The cement type coatings fail when the complete covering of glass fabric or mat is omitted, since volatilization of the preservative oils actually cracks and blows the cement from the surface of the timber. Complete coverings of glass fabric are very expensive from the standpoint of initial cost and especially from the standpoint of labor cost for application.

The improved coating and method of proong which constitute the instant invention eliminate all the difficulties heretofore outlined and a large measure of efficiency is derived from cooperation with the volatilizing characteristic of the preservative fluid which heretofore has created the primary difficulty in producing a satisfactory freproof coating.

For a better understanding of the invention, reference may be had to the accompanying drawing, in which:

Fig. 1 is a cross section View of the article of the instant invention with legends describing the elements thereof, the preservative material and the coating material being enlarged in thickness for clarity; and

Fig. 2 is a flow diagram of the process used in producingthe article of Fig. 1.

A coating which I have found eminently satisfactory for accomplishing the above described objectives is comprised primarily of a sodiiun silicate solution with the addition of some mineral filler such as slate dust, fibrous talc, or ground limestone, and 4asbestos fibers. Preferably a sodium silicate solution of 42.2 Beaurn (approximately 38%' by Weight) and having an alkali to silica ratio of 1:3.22 is utilized. A satisfactory formulation is as follows:

Percent 42.2 Beaum sodium silicate solution 60 Mineral filler (slate dust or fibrous talc) 35 7R asbestos bers 5 The above composition is of brushing or spraying consistency. If need be, it may be thinned slightly with water, but dries to form a hard coating due to the evaporation of water from the silicate solution.

Sodium silicates are non-inflammable and their use in tire-proofing compositions may not per se be novel. However, when utilized in conjunction with timber or wood which has been treated with preservative lluid in the manner heretofore described, a most unexpected and beneficial cooperative relationship develops which results in a complete solution of the various problems heretofore outlined.

`The silicate coating softens at approximately 1050 F. When the coating is exposed to fire it begins to soften slightly at about 1050 F. and continues to get softer up to approximately 1575" F., at which point it is softest. As the coating becomes soft, or just before it softens completely, the heat which causes such softening produces the formation of an excessive amount of gas from the preservative oils due to volatilization thereof. With this volatilization and evolution of gas the coating expands and swells in much the same manner as hot glass that is being blown by a glass blower.

As the silicate coating under the influence of heat expands away from the timber, in some cases as much as two inchesor more, it remains intact and the temperature 'at' the surface of the Vwood drops greatly, becoming suciently low'to prevent destructive distillation and ,charring of the wood.

' 'The reduced temperature adjacent the surface of the Iimpregnated wood slows down the volatilization of the `oils considerably. Nevertheless, the heat absorbed within "the timber continues to provide sufficient gas evolution to force the gas through pin-hole openings which develop in fthe surface vof the expanding'coating. These pin holes permit diffusion of the gases into the atmosphere snrrounding the coated timber.

Y Thevolatilization characteristics of the impregnating composition continue so long as any fire is present at the outer surface of the coating, due to the low flash point of :the said composition. This continued evolution of v 4gas fromadjacent the timber surface excludes oxygen from the void or space created by expansion ofthe coating v VVfrom the timber. .Thus there is no possibility of the tim- ,ber itself burning. Even if an opening an inch or two in' diameter should occur in the coating, by mechanical or accidental causes, gases from the preservative oils are .Under some circumstances it has been found advisable lto add a small proportion of emulsied asphalt to the 4sodiumsilicate composition for the purpose of increasing the tensile strength of the coating'and its stability in supporting loads where used on piles and other structuralun'its adaptedrto serve that purpose.

.Since sodium silicate is water soluble, it should be lproofed against weather and'watei in some way where the timber or wooden structural unit is to be used for purposes which have heretofore been suggested.'V For some purposes it may be suflicient to add a waterprooing agent to the sodium silicate solution, but it is preferable to apply over, the surface of the silicate base coating a :regular asphaltum base coating of the type generally used for roof coatings. Such a coating, like the sodium silicate base coating itself, may be applied by brush or spray.

A preferred sodium silicate coatingr has been discovered; its properties have been proved superior through extensive Y tests..A This preferred coating, when protected by a vinyl valuminum weatherproof coating, has gone a period of 2,000 hours in the weatherometer and when tested by tire still shows good expansion properties. The formulation is as follows:

Percent ,42.2"V *Beaum sodium silicate solution 42.0 `Slatedust or other suitable mineral pigment 22.0 7R asbestos bers 6.0 vEmulsifed asphalt, 53% solids as asphalt 30.0

This formulation must be mixed in a special manner; the sodium silicate, slate dust, and asbestos must be mixed first and then the emulsified asphalt is added.

The vinyl aluminum weatherproof coating used to protect the preferred sodium silicate coating has the following Y fThe aluminum powder used in this coating has a-maxi- Vmurnretentiony of 15% on a 325 mesh screen. It has a bulking value of 0.0.47 gallon per pound and a weight of `21.24 pounds per solid gallon'. The vinyl chloride-vinyl ,acetate f copolymer H resins Vhave lsutiicient chlorine in them fsuicient to block the hole and prevent any combustion Y from occurring beneath the level `,of the expanded coating.

CTI

Y to prevent the coating from supporting combustion exceptv when it is in the presence of fire.

A sodium silicate coating may bc applied directly to Va freshly treated wood structure since the sodium silicate is not affected by the preservative material in the structure such as creosote and petroleum oils. Y

In certain structures it is not commercially feasible and sometimes not possible to cover completely the sodium silicate coating with a weatherproof coating. It has been discovered in practice that, where the sodium silicate tireproof coating is not completely covered, water will-deleteriously affect not only the uncovered fireproof coating but also a portion of the covered tireproof coating by a leaching action from under the weatherproof coating. Fire retardant materials for coatings which do not require the protection of a weatherproof coating and which have the quality of binding mineral pigments together when properly formulated to give the desired expansive coating'are as follows:

Vinyl 'resins Chlorinated asphalt Chlorinated parain f A preferred material for the' formulation of a tire retardant weatherproof coating which,`.like sodium silicate,

may be applied directly to a Vfreshly treated wood structure is the polyvinylacetate resin sinceV it is not affected by the fcreosote and petroleum oilpreservative. Polyvinyl acetate resins, as well as the vinyl-vinylidene resins,

.are presently commercially available as water emulsionsV and therefore offer the added-advantageof non-inflam- Vmability. 1

A very effective expansive coating-is Vprepared by the addition t-o Ia polyvinyl acetate resin of suitable Iamounts of a lplasticizer, solvents, thckeners, mineral pigments .and water as a diluent. The V,carboxyl group contained in the chemical structure of the polyvinyl acetate resins forms carbon dioxide when burned, `and this gas formation greatly retards the rate of -burning Vof the resins. Thus this material, when plasticized with 4a tire-retardant plasticizer such as tr'icresyl phosphate, functions most VsatisfactorilyV as a Ibinding resin in yan expansive coating.

A vsuitable and preferred polyvinyl acetate-type coating is a-sfollows:

.9.21% polyvinyl acetate Resin. Y V1.57% 'tricresyl phosphate Plasticizer. Y 2.32% ethylene glycol mono- Y vethyl ether 1 rFilm forming' solvent. 0.26% dioctyl sodium solfosuccinate Wetting agent. 0.'21%`po1yoxyethylated vegel Y Y Y, table oi1 igment dispersion aid.

`0.33% 400 centipoi'se methyl g ce1lulose Thickener. 1 0.41% sodium pentachloro- Y Y p henate.l 1 Preservative. 28.72% talc Mineral pigment. 2.74% carbon blacku'. Pigment.

'0.27% oleic acid:0.2 2% 26 am- Y monia (ammonium oleate) Buifering agent to give VVpH of 8-9.

The polyvinyl acetate used in this coating comes in vthe form of an emulsion and the percentage shown is the actual solids content of the emulsion used in the coating and the Water used in making the emulsion is shown in the total percentage of Water. Since this coating is an emulsion it can be brushed or sprayed right over the oily surface of timber containing preservative oils, and i-t is not affected, i. e., is not softened by the preservative oils, and dries to a firm, hard coating by the evaporation of the Water. This coating may also be thinned with Water, which is advantageous.

A preferred coating having the desired expansible properties coupled with suicient chlorine in its make-up to render it very lire retardant includes a chlorinated rubber and a 70% chlorinated paraliin, a 40% chlorinated paraffin being included also primarily as a plasticizer. A preferred formulation is as follows:

Percent Chlorinated rubberviscosity of 125 centipoises 5.70 70% chlorinated paraiiin 5.70 40% chlorinated paraliin 5.70 Toluene 14.40 Methylethylketone 12.05 Xylene 4.00 7R asbestos iibers 6.26 Slate dust 41.96 Carbon black 3.72 Stabilizer 0.51

The 'above solvent coating material maybe changed to an emulsion coating material by the replacement of most `of the solvents with water. The product is made by dissolving the chlorinated rubber and the two types ofi chlorinated paraffin in the solvents shown and stirring into this solution the asbestos and slate dust. The resultant coating is a viscous semi-Huid material suitable for applying with brush or spray equipment.

A coating employing chlorinated rubber and chlorinated parafn when used on freshly treated oily wood structures does not give the superior `results of the previously discussed sodium silicate type or the polyvinyl facetate type. The preservative oils `are quite readily soluble in the solvent used for the chlorinated rubber and chlorinated paraflin; therefore any residue oil -on the surface or any oil which might bleed to the surface due to heat from the sun will be absorbed into the coating. A coating employing chlorinated rubber and chlorinated parafiin is well suited for oil-free surfaces of structures having impregnated oils in an amount suficient to cause eX- pansion of the coating When heated by tire but insuicient to cause bleeding when heated by the sun.

A Acombination chlorinated material-alkyd resin type coating has been discovered which provides the solution to this problem; it has the property of a much greater resistance to the preservative oils in the Woods since the dried alkyd resin can stand the 4absorption of a reasonable amount of preservative oil Without allowing softening of the coating. A preferred chlorinated rubber-alkyd resin coating material is as follows:

Percent Chlorinated rubber 7.00 Alkyd resin 5.00 Slate dust 41.25 7R asbestos 7.00 Lead naphthenate 0.33 Cobalt naphthenate 0.08 Manganese naphthenate 0.04 Stabilizer 0.50 Solvent (toluene or xylene) 35.05 Carbon black 3.75

Alkyd resins which are unmodified by drying oils are composed of glycerol and phthalic anhydride. When these two products are heated together, they react to form a long chain molecule which has available hydroxyl groups on it. These hydroxyl groups may be reacted with unsaturated monoacids `such as linoleic acid Vwhich is one of the main constituents of linseed oil. Linseed, tung, perilla, sh, oiticica, and soybean oils can be used as modifying oils for 4the alkyd resins. The oil used in modifying-alkyd resins must be one which will make the finished alkyd resin compatible with chlorinated rubber. A suitable alkyd resin for this use generally contains approximately 23% to 29% phthalic anhydride, the remaining portion being glycerol 1and drying oil.

In coatings employing chlorinated rubber and chlorinated paraii'ins, stabilizers are required for the chlorinated materials. These stabilizers are primarily for the purpose of preventing dehydrochlorination when exposed to ultra-violet light. rPhe addition of carbon black pigments or other suitable pigments to filter out the ultra-violet light is helpful and, in addition, gives color to the coating. Other suitable stabilizers are monohydrous tribasic lead sulfate, basic lead silica-te sulfate, dibasic lead phosphite, dibasic lead phthalate, and the alkaline earth metal salts of such acids as stea'ric, oleic and ricinoleic acids.

In all coatings numerous types of mineral pigments may be used either singly or in combination, examples being asbestos fibers, talc, slate dust, ground limestone, finely ground mica, and finely ground perlite, either in expanded or unexpanded form.

Materials which function as plasticizers and 'are exceptionally fire-retardant are (l) tricresyl phosphate, (2) liquid chlorinated biphenyl and polyphenyl and (3) 40% chlorinated paraffin. It will be understood that other plasticizers might well be used and that in some -situations any resin which is not fire-retardant might be substituted in `small percentages for the lire-retardant resin, especially when the plasticizer is an exceptionally good fire retardant.

As has previously been stated, the desired expansive property may` be obtained by the proper application of the coating materials. Coating materials of the sodium silicate type have exceptionally good expansive and fireretardant qualities; a weatherproofing outer coat is required to prevent deterioration by water.. The polyvinyl acetate type coating and the chlorinated rubber type coating have good expansive `qualities. and may be used Without an outer weatherproong coat.

In all of the coatings based upon the chlorinated rubber, :chlorinated paraffin and polyvinyl acetate, it will be noticed that there is a very large percentage of mineral pigment which when bound by a small percentage of `the resin forms the desired expansible wall to provide a chamber between the fire and the wood. The resin may or may not decompose, depending upon the intensity of the fire. If it does decompose, the resulting partially decomposed resin and carbon formed from the decomposition of the resin, act as the binding material, `after expansion has occurred.

In certain locations it has been found advisable to restrict the degree of expansion of the lire-retardant coating; this has beenfound of value when using coatings of the chlorinated rubber type and the polyvinyl acetate type. lIn tests, glass fabric strips which are three inches wide have been stapled to timbers to reduce the expansion of the coating and to increase the mechanical bond strength of the coating to the wood, this being of prime advantage on freshly treated timbers. For round timbers, such as piles or posts, the three inch glass fabric strip is spirally wound yon the timber at l2 inch centers. At no point does the coating extend more than 9 inches, thereby reducing expansion. For large flat surfaces the glass fabric may be spaced at 12 inch centers. On small rectangular timbers, stripping of the corners has proved a satisfactory expedient.

On rather dry, weathered timbers stripping is not required, except on the corners, since the volatilization of v the remaining preservative oils is usually not suiiicient to excessively expand the coating.

In some situations it may be desirable to insure the production of gases under the coating. Old weatherbeaten timbers,igunpreserved Wood structures, plastic Vstructures and.=metal structures, the thinsheet 'metal type, forexample, caribe coated withftheV rep'roof coatingsgof my invention. Thedesired expansion property of the coating maybe obtainediby applying `an undercoat `capable of producingY the required amount of gas. A 'suitable under- 'coat can be formulated by dispersing 10% to 15% of the structureand the lire. It wi-ll be appreciated that the degree of expansioncan be controlledwithin reasonable Vlimits by applying a predetermined amount of ithe gasproducing undercoat. Y Y While I have describedfor illustrative .purposes a p-re- -ferred form of the invention, various modications Within v itsiscope may be apparent to those skilledin the artV and for that reason' I wish to limit myself only Within the scope ofthe appended claims. Y l'claim:A Y Y Y 1. A structural unit comprising astructural member, preservative material including a petroleum oil combined c with said structural member, Iand a coating coveringsaid structural `member and said preservative material for inhibiting deterioration and destruction by firey of said structural member, said coating comprising a'thermoplastic material -selected from the group consisting of sodium silicate, polyvinyl acetate resin, chlorinated rubberchlorinated parain, and chlorinated rubber-alkyd resin, said coating having the property of becoming soft and elastic under heat, sai-d preservative material including a petroleum oil having the property of producing an excessive amount of -gas as the coating softens due to heat to cause expansion of said Vcoating by the formed gas away from -said structural member to form an insulating chamber over said structural member.

2. A structural unit comprising a wood'rnember, a pre# servative material including a preservative oil impregnated intosaid wood member, and a coating covering said wood member and said preservative material for inhibiting dev terioration yand 4destruction by lire of said Wood member,

said coating comprising a thermoplastic material Yincluding polyvinyl acetate resin, said coating having the property `of becoming soft and elastic under heat, said preservative Vmaterial'.including a' petroleum oil having'the `property of producing an excessive amount of ga's'as the'Y coat- -ing softens Adue 'toheat to' cause .expansion of said'coating :bythe 'formedfgas away from vsaid;vV/oodinernber to 'form an :insulating:chamberV overjsaid iwgood member.

3. A method of Vpreserving andriireprodtinga structural member ywhich comprises thesteps f combining 'a prematerial withra coating comprising a thermoplastic map terial selected from the lgroup consisting of sodium sili- Y 'cate,1polyvinyl :acetate resin, vchlorinated rubber-chlorinated Vparaflin,and chlorinated Vrubber-alkyd '.res'injfand drying "the 'coating to 'form 'a hard ,coating having the Y property of becomingsoft'andlela'sticunderlieat whereby said coating is caused to expand avv-ay from said structural member byf the .formed gas of said preservative material, the .expansion of .said coating for-ming an insulatingachamberlover the structuralmember. l Y

4. AV method ofvpreservingv and Aireprooiing a wood memberwhichvcomprises the steps of combining Vapreservative.materialincluding a petroleumroil with thewood member, said preservative material having the property o'fcprodu-cing annexcessive amount of gas when'heated, coating the wood member and preservative material withv a coating vcomprising a thermoplastic material including polyvinyl acetate resin, and drying the coating Vto form arhard coating having the property of becoming soft and elastic under heat whereby said coating is caused to exp'and away from said wood member by thefformedgas of saidpre'servative material, the expansion of said coating forming an insulating :chamber over the wood member.

References Cited inthe tile of this patent UNITED STATES PATENTS 2,650,206' Stock" r Aug.25, V1953 

1. A STRUCTURAL UNIT COMPRISING A STRUCTURAL MEMBER, PRESERVATIVE MATERIAL INCLUDING A PETROLEUM OIL COMBINED WITH SAID STRUCTURAL MEMBER, AND A COATING COVERING SAID STRUCTURAL MEMBER AND SAID PRESERVATIVE MATERIAL FOR INHIBITING DETERIORATION AND DESTRUCTION BY FIRE OF SAID STRUCTURAL MEMBER, SAID COATING COMPSRISING A THERMOPLASTIC MATERIAL SELECTED FROM THE GROUP CONSISTING OF SODIUM SILICATE, POLYVINYL ACETATE RESIN, CHLORINATED RUBBERCHLORINATED PARAFFIN, AND CHLORINATED RUBBER-ALKYLD RESIN, SAID COATING HAVING THE PROPERTY OF BECOMING SOFT AND ELASTIC UNDER HEAT, SAID PRESERVATIVE MATERIAL INCLUDING A PETROLEUM OIL HAVING THE PROPERTY OF PRODUCING AN EXCESSIVE AMOUNT OF GAS AS THE COATING SOFTENS DUE TO HEAT TO CAUSE EXPANSION OF SAID COATING BY THE FORMED GAS AWAY FROM SAID STRUCTURAL MEMBER TO FORM AN INSULATING CHAMBER OVER SAID STRUCTURAL MEMBER. 